Inhibitors for acid solutions employed in the surface treatment of metals



Alan

United States Patent INHIBITORS FOR A'CID SOLUTIONS EMPLOYED IN THESURFACE TREATMENT OF METALS Wennemar Strauss, Dusseldorf-Benrath, AlfredKirstahler, Dusseldorf, Wolfgang Giindel, Dusseldorf- Oberkassel, andWolf-Dieter Willmund, Dusseldorf- Holthausen, Germany, assignors toDehydag, Deutsche Hydrierwerke G.m.b.H., Dusseldorf, Germany, acorporation of Germany No Drawing. Filed Feb. 9, 1955, Ser. No. 487,224

Claims priority, application Germany Feb. 10, 1954 7 Claims. (Cl.252-149) i aftentea. Oct. 18, 196d 'ice . hibitors which possess all oftheabove characteristics.

This invention relates to inhibitors for acid solutions employed in thesurface treatment of metals, and more particularly to organic sulfonicacid compounds and their use as inhibitors in the surface treatment ofmetals with acid agents.

The treatment of metal surfaces with acid agents is well I known inindustry and is frequently referred to as pickling. For example, priorto the application of coatings or electrodeposits to metal surfaces, andsometimes Prior to machining Working metal P it is "".2 lined above. Thebivalent hydrocarbon radical R in the necessary to remove dirt, grease,rust or the like which may have accumulated on thesur faces duringhandling or storage. For this purpose, the metal objects, such as, forexample, iron or steel objects, are immersed into acid solutions,particularly into more or less concentrated solutions of mineral acidsor their acid salts which are often called pickling liquor. The same orsimilar processes are used for cleaning other metals, such as zinc oraluminum. The acid solution readily dissolves or removes any extraneousmatter adhering to the metal surface and exposes the clean, uncorrodedmetal. However, if the metal object is not promptly withdrawn from theacid bath after all the dirt, grease, rust and the like have beenremoved and the bare metal is exposed, the acid agent or pickle liquorwill begin to attack the metal itself.

Many methods for preventing the attack of the clean metal by the acidpickling agent have been proposed. The most common method is to modifythe acid solution with various additives which form a protective layeron the clean metal surface and thereby prevent the acid agent fromattacking the bare metal. Such additives are known in the art asinhibitors.

A great number of compounds have been found to be etfective asinhibitors. However, while the individual inhibitors known to the priorart possess certain desirable characteristics which make them suitablefor special purposes, for use in only certain particular acid baths, orfor use with only certain types of metal, the prior art fails todisclose inhibitors adapted for substantially universal use.

Modern practice in the art of treating the surfaces of metals with acidsolutions requires not only that the inhibitor give a maximum degree ofprotection against attack by the acid solution on the virgin metal atrelatively low concentrations of inhibitor, but also that the inhibitorhave a lasting eliect, i.e. that the inhibitor be resistant againstdecomposition under the operating conditions and l ahigh grade moderninhibitor should not generate gases 5 Another object of the presentinvention is to provide inhibitors which may be employed universally inall types of acid baths and in conjunction with a wide variety ofmetals.

Other objects and advantages of the present invention will becomeapparent as this description proceeds.

We have found that organic sulfonic acids having the general structuralformula wherein X represents a halogen atom or an atom group chemicallyrelated to halogen, such as a cyanide group or a thiocyanide group, forexample, and R representsa bivalent aliphatic,*cycloaliphatic oraromatic radical, or their salts, have excellent?corrosion-preventingproperties and may be used as inhibitors in acid solutions for thetreatment of metal surfaces. When used as inhibitors in such solutions,these compounds have all of the desirable characteristics which modernpractice demands, as outgeneral structural formula may be anunsubstituted radical or it may carry substituents such as alkylradicals, oxy- "groups, .nitro-groups, additional sulfonic acid radicalsand/orhalog'en atoms, cyano-groups or thiocyano-gronps;

Representative examples of sulfonic acids which may advantageously beused, as inhibitors as such min the form of their salts in accordancewith our invention are the following:

Chloromethanesulfonic acid Bromomethanesulfonic acid Iodomethanesulfonicacid Dibromomethanesulfonic aci'd 2-chloro-ethanesulfonic acid-12-bromo-ethanesulfonic acid-1 2-cyano-ethanesulfonic acid-12-thiocyano-ethanesulfonic acid-1 3-bromo-propanesulfonic acid-14-bromo-butanesulfonic acid-l 4-bromo-butanesulfonic acid-23-iod0-propanesulfonic acid-1 3-cyano-propanesulfonic acid-l4-thiocyano-butanesulfonie acid-l 2,3-dichloro-propanesulfonic acid-l6-bromo-hexanesulfonic acid-l 3-bromo-camphor-sulfonic acid-72-chloro-benzenesulfonic acid-1 3-chloro-benzenesulfonic acid-14-chloro-benzenesulfonic acid-1 2,3-dichloro-benzenesulfonic acid-12,4,5-trichloro-benzenesulfonic acid- 1 7 4-bromo-benzenesulfonic acid-16-chloro-3bromo-benzenesulfonic acid-1 2,4-dibromo-benzenesulfonicacid-1 2,-5-dibrorno-benzenesulfonic acid-13,4,5-tribromo-benzenesulfonic acid-1 2,3,4,S-tetrabromo-benzenesnlfonicacid-l 4-iodo -benzenesulfonic acid-l 4-chloro-3-nitro-benzenesulfonicacid-1 5-bromo-2-nitro-benzenesulfonic acid-1 4-chloro-toluenesulfonicacid-2 4-bromo toluenesulfonic acid-2 4-iodo-toluenesulfonic acid-'23,4,5-trichloro-toluenesulfonic acid-2 4 chloro-toluenesulfonic acid-3 12-chloro toluenesulfonic acid-4i 6-bromo-toluenesulfonic acid-32,4-dichloro-toluenesulfonic acid-4 2-bromo-toluenesulfonic acid-44-Chl010-b6I1Zyl-w-SU1fOIliC acid 4-bromo-benzyl-w-sulfonic acid5-bromo-o-xylenesulfonic acid-4 2,6-dichloro-m-xylenesulfonic acid-44-chloro-naphthalenesulfonic acid-l 4-bromo-naphthalenesulfonic acid-14,7-dichloro-naphthalenesulfonic acid-l l-chloro-naphthalenesulfonicacid-2 6 bromo-naphthalenesulfonic acid-25,8-dibromo-naphthalenesulfonic acid-2 4-brorno-toluene-di-sulfonicacid-2,6 4-bromo-naphthalene-di-sulfonic acid-2,74,4-dibromo-diphenyl-disulfonic acid-2,2 2-chloro-phenolsulfonic acid-42-bromo-phenolsulfonic acid-4 2,6-dichloro-phenolsulfonic acid-42,6-dibromo-phenolsulfonic acid-4 2,6-di-iodo-phenolsulfonic acid-46-bromo-phenol-di-sulfonic acid-2,4 6-bromo-naphthol-l-sulfonic acid-38-bromo-naphthol-l-di-sulfonic acid-3,5 l-bromo-naphthol2-sulfonicacid-8 The organic sulfonic acid compounds can be used as inhibitors inthe manner customary in the art of treating the surface of metals withacid agents. The amounts of inhibitor added to acid baths may varywithin wide limits and depend upon the composition of the acid bath,upon the metal to be treated and sometimes also upon the temperature ofthe acid bath. In general, however, it is sufficient to add between0.01% and 0.5% by weight of organic sulfonic acid inhibitor, based uponthe amount of acid agent used.

Acid solutions modified in this manner may be used for extended periodsof time without any loss of effectiveness of the inhibitor. Suchmodified solutions are also effective over wide temperature ranges andmay be used in conjunction with virtually any metal which is customarilysubjected to a surface treatment, such as, for example, iron, zinc,aluminum and the like. The organic sulfonic acid inhibitors arenon-poisonous, will not escape with the steam or acid vapors generatedby such acid solutions, and are virtually free from objectionable odors.In addition, the inhibitors used according to our invention do notgenerate gases which tend to interfere with the surface treatment of themetal. In other words, the organic sulfonic acid compounds having theabove general structural formula represent inhibitors which individuallycombine all of the desirable characteristics required of high gradeinhibitors in modern practice.

Moreover, the inhibitors described above are readily compatible withknown inhibitors and may be used either in conjunction therewith oralone.

Acid solutions which may be modified with the organic sulfonic acidinhibitors in accordance with our invention include solutions of mineralacids and mineral acid salts, as well as organic acids.

Solutions modified with such inhibitors can advantageously be employedin a variety of surface treatments of metals, such as, for example,cleaning, pickling, etching, sealing and the like.

The following example will further illustrate our invention and enableothers skilled in the art to understand our invention more completely.It is understood, however, that the example is given only for thepurpose of illustration and that our invention is not limited thereto.

Example Two sections of sheet iron, each having a surface area of about18 cm. were placed into a 4 N solution of hydrochloric acid and a 4 Nsolution of sulfuric acid, respectively. The attack of the acid uponeach of the sections was recorded by measuring the amount of hydrogengiven oif. The temperature of the acid baths was maintained at 60 C. Therate of corrosion of each metal section thus determined furnished acontrol value to which the rates of corrosion of acid baths modifiedwith organic sulfonic acid inhibitors in accordance with our inventioncould be compared to determine the effectiveness of such inhibitors.

Identical sections of sheet iron were then placed into 4 N solutions ofhydrochloric acid and 4 N solutions of sulfuric acid which were modifiedwith 1 gm./ liter of various representative organic sulfonic acidinhibitors such as described above. The amount of hydrogen generated byeach solution was again recorded. The following table shows the type oforganic sulfonic acid compound used and its corrosion-preventing effectin 4 N hydrochloric acid and 4 N sulfuric acid, expressed in percent ofcomplete prevention based upon the control values obtained fromunmodified acid baths, as described above.

Corrosion-preventing effect in percent Inhibitor added In each case thepickling, or cleaning, effect of the acid on unclean or rusted metalsurfaces was the same but in the baths using our new inhibitors theattack of the acid on the virgin metal surfaces as compared with theattack by the uninhibited acid was reduced by the percentage given. Eachof the materials listed earlier as representative examples of materialswhich may be used as inhibitors according to our invention, and othermaterials coming under the general structural formula previously setforth, will show similar corrosion-preventing effects in acid picklingbath.

While we have given certain specific embodiments of our invention, wewish it to be understood that the invention is not limited to suchembodiments and that various changes and modifications can be madetherein without departing from the spirit of the invention or the scopeof the following claims.

We claim:

1. The method of preventing acid corrosion of the metal during thepickling with a mineral acid pickling bath wherein the mineral acid isselected from the group consisting of hydrochloric and sulfuric acids,of metal surfaces subject to corrosion by mineral acids, which consistsof adding to said mineral acid pickling bath from 0.01% to 0.5% byweight, based on the amount of said mineral acid in said pickling bath,of an inhibitor selected from the group consisting of compounds havingthe general structural formula and their sodium salts, wherein X is aradical selected from the group consisting of chlorine, bromine, iodine,cyanide and thiocyanide, and R is a lower aliphatic radical containingfrom 1 to 6 carbon atoms.

2. The method of preventing acid corrosion of the metal during thepickling with a mineral acid pickling bath, wherein the mineral acid isselected from the group consisting of hydrochloric and sulfuric acids,of metal surfaces subject to corrosion by said mineral acids, said metalbeing selected from the group consisting of zinc, aluminum, iron and itsalloys, which consists of adding to said mineral acid pickling bath aninhibitor in the amount of from 0.01% to 0.5%, based on the amount ofsaid mineral acid in said pickling ath, elected from and their sodiumsalts, wherein X is a radical selected from the group consisting ofchlorine, bromine, iodine, cyanide and thiocyanide, and R is a bivalentlower alkyl radical containing from 1 to 6 carbon atoms.

3. The method of preventing acid corrosion of the metal during thepickling with a mineral acid pickling bath, wherein the mineral acid isselected from the group consisting of hydrochloric and sulfuric acids,of metal surfaces subject to corrosion by said mineral acids, said metalbeing selected from the group consisting of zinc, aluminum, iron or itsalloys, which consists of adding to said mineral acid pickling bath aninhibitor in the amount of from 0.01% to 0.5%, based on the amount ofsaid mineral acid in said pickling bath, consisting of the sodium saltof a compound having the general structural formula wherein X is aradical selected from the group consisting of chlorine, bromine, iodine,cyanide and thiocyanide, and R is a bivalent lower aliphatic radicalcontaining from 1 to 6 carbon atoms.

4. The method of preventing acid corrosion of the metal during thepickling with a mineral acid pickling bath, wherein the mineral acid isselected from the group consisting of hydrochloric and sulfuric acids,of metal surfaces subject to corrosion by said mineral acids, said metalbeing selected from the group consisting of zinc, aluminum, iron and itsalloys, which consists of adding to said mineral acid pickling bath aninhibitor in the amount of from 0.01% to 0.5% based on the amount ofsaid mineral acid in said pickling bath, consisting of the sodium saltof a compound having the general structural formula wherein X is achlorine atom and R is a bivalent lower aliphatic radical containingfrom 1 to 6 carbon atoms.

5. The method of preventing acid corrosion of the metal during thepickling with a mineral acid pickling bath, wherein the mineral acid isselected from the group consisting of hydrochloric and sulfuric acids,of metal surfaces subject to corrosion by said mineral acids, said metalbeing selected from the group consisting of zinc, aluminum, iron and itsalloys, which consists of adding to said mineral acid pickling bath aninhibitor in the amount of from 0.01% to 0.5%, based on the amount ofsaid mineral acid in said pickling bath, consisting of the sodium saltof a compound having the general formula wherein X is a bromine atom andR is a bivalent lower aliphatic radical containing from 1 to 6 carbonatoms.

6. The method of preventing acid corrosion of the metal during thepickling with a mineral acid pickling bath, wherein the mineral acid isselected from the group consisting of hydrochloric and sulfuric acids,of metal surfaces subject to corrosion by said mineral acids, said metalbeing selected from the group consisting of zinc, aluminum, iron and itsalloys, which consists of adding to said mineral acids an inhibitor inthe amount of from 0.01% to 0.5%, based on the amount of said mineralacid in said pickling bath, consisting of the sodium salt of a compoundhaving the general structural formula wherein X is an iodine atom and Ris a bivalent lower aliphatic radical, containing from 1 to 6 carbonatoms.

7. A mineral acid pickling bath solution for pickling the surface ofmetal objects subject to attack by mineral acid, comprising a mineralacid selected from the group consisting of hydrochloric and sulfuricacids and from 0.01% to 0.5% by weight, based on the amount of saidmineral acid in said pickling bath of an inhibitor, selected from thegroup consisting of compounds having the general structural formula XRSOH and their sodium salts, wherein X is a radical selected from the groupconsisting of chlorine, bromine, iodine, cyanide and thiocyanide, and Ris a bivalent lower aliphatic radical containing from 1 to 6 carbonatoms.

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